The XiaoIce system [1]} rewrites questions using the long conversation history which might span a few days or months. To do so, it requires to explicitly track the dialog history to identify and store named entity mentions and predicates from previous conversation turns produced by the user and the system. XiaoIce’s CQR component consists of three modules. It rewrites \(Q\)  to \(\hat{Q}\)  using \(\mathcal {H}\)  in three steps.
